This invention relates to foamed plastics material and, more particularly, to a process for the manufacture of polyurethane (including polyisocyanurate) foams as well as to the foams themselves.
It is well known to manufacture such polyurethane foams by reacting an organic polyisocyanate (including diisocyanate) with slightly less than a stoichiometric amount of an organic polyol in the presence of a volatile liquid blowing agent which is caused to vaporize under the influence of the heat generated by the reaction between the polyisocyanate and the polyol. The vaporization of the blowing agent causes cells to grow in the liquid reaction mixture. As the reaction proceeds, the viscosity of the liquid increases, finally forming a solid polyurethane foam.
It is also generally known to use blowing agents which are gaseous at atmospheric conditions but which are held in a condensed form by maintaining the reaction mixture under pressure. In such case, vaporization of the blowing agent occurs when the pressure is released, with the reaction mixture then expanding to form a foam which subsequently cures to become the polyurethane foam.
It is also known to combine the above two types of blowing agent to provide part of the expansion before the exotherm develops. In this way, a foam may be formed and added to an enclosed cavity with less subsequent expansion and pressure build up from the reaction exotherm expansion than a foam blown exclusively due to the reaction exotherm.
Polyisocyanurate foams are similarly prepared except a larger excess of isocyanate over hydroxyl groups is used. Generally, formulations with an isocyanate index (the ratio of isocyanate groups to hydroxyl groups) of 1.5 or more along with certain catalysts, form foams with isocyanurate groups along with urethane groups. These foams will be referred to as polyisocyanurate foams. Isocyanurate groups result in a more cross-linked foam since they are formed from the reaction of three isocyanate groups. ##STR1##
Typical blowing agents are the various chlorofluorocarbons (CFC). Throughout this specification the following symbols are used with respect to blowing agents: CFC-11 (or I-11) refers to CCl.sub.3 F, CFC-113 (or I-113 ) refers to CCl.sub.2 FCClF.sub.2, CFC-12 (or I-12) refers to CCl.sub.2 F.sub.2, CFC-142b (or I-142b) refers to CH.sub.3 CClF.sub.2 , CFC-114 (or I-114) refers to CClF.sub.2 CClF.sub.2 and CFC-22 (or I-22) refers to CHClF.sub.2.
The present invention permits usage of higher levels of aromatic polyesters polyols (hereinafter referred to as "APPs") in the polyol component. Such higher levels of aromatic polyester polyols have the advantages of lower costs with respect to the portion of the polyol component that it replaces, as well as providing a product of lower combustibility levels and a product that is less brittle. More detailed characteristics of these polyols are discussed in the literature (See, e.g., Proceedings of the SPI-28th Annual Technical/Marketing Conference, Technomic Publ. Co., Lancaster Pa., 1984, pp. 40-65).
Applicant's invention includes substitution of CFC-22 for at least a portion of the conventionally used CFC-12 and/or CFC-11 blowing agent which enables the proportion of the aromatic polyester polyol in the polyol component to be increased.
Heretofore the fraction of the aromatic polyester polyol in the polyol component has been undesirably limited because of the inadequate solubility of the required frothing and blowing agents in the polyol component. The solubility limitation is particularly acute with CFC-12, which is the most frequently used blowing agent for pre-expanding the polyol/isocyanate formulation before the exotherm from the reaction of the two components expands the primary blowing agent, typically CFC-11. In formulations wherein CFC-12 must be dissolved along with CFC-11 under pressure in the polyol component of the formulation, the level of aromatic polyester polyol which can be used is very limited because of the solubility limitation, manifested typically by separation of the liquid phase.
Most rigid polyurethane foams incorporated other types of polyols ("copolyols") in addition to the aromatic polyester polyol in the formulation to achieve adequate physical properties such as improved dimensional stability during aging tests at high humidity. Usually these copolyols have higher functionality for higher degrees of cross-linking and exhibit improved compatibility with CFC-11, but the copolyols are far more expensive than the aromatic polyester polyols and contribute less to fire retardancy. Use of a larger amount of aromatic polyester polyol as allowed by practice of the invention, which replaces the higher cost polyols (typically propoxylated/ethoxylated sucrose derivatives) lowers overall foam costs while providing a product that is less brittle.